The colors below represent a close approximation of the actual pen colors. It must be kept in mind that plastic colors were mixed in different batches as production warranted and thus, some degree of variation in shades is to be expected. This is especially true in the Vacumatic "51" colors, such as the grays and cordovans. In addition, the earlier pencils were made out of celluloid instead of lucite. The pencils will discolor to a darker shade than the pens, to the point that they no longer appear as a matched set. This can become very pronounced in the grays, which will almost turn a translucent green and the cedar blues which can turn nearly black. Celluloid plastic will also become brittle over time and will tend to crack if stressed.